A line scan type ink jet recording device has been proposed as a high-speed ink jet recording device for printing on recording sheets at high speed. The device has an elongated ink jet recording head that extends across the entire width of the recording sheet. The recording head is formed with a row of nozzle orifices through which ink droplets are ejected. Ink droplets are ejected through the nozzle orifices of the recording head that confronts the recording sheet while performing a main scan to consecutively move the recording sheet. “Main scan” means scanning movement of the recording sheet in the movement direction. Lines extending in the main scan direction on the recording sheet that the nozzle orifices confront are referred to as “main scan lines”. By this type of control, recording dots are selectively formed on the scan lines of the recording sheet.
Line scan type ink jet recording devices include those that use continuous type ink jet recording head and those that use on-demand type ink jet recording heads. Although on-demand type ink jet recording devices do not record as quickly as continuous type ink jet recording devices, they are appropriate for a popularized high-speed recording device for reasons such as the ink system is extremely simple.
Japanese Patent Application Publication No. HEI-11-78013 discloses an example of recording heads used in on-demand type ink jet recording devices. The recording head is formed with a row (line) of nozzles, wherein the nozzles are in a one-to-one correspondence with main scan lines of the recording sheet. That is, a number of the nozzles is the same as the number of the main scan lines. Each nozzle has an ink chamber opened with the nozzle orifice. Pressure is applied to the ink in the ink chambers by applying a drive voltage to thermal elements or piezoelectric elements, so that ink droplets are ejected through the nozzle orifices. With this configuration, high-speed recording devices having a simple configuration can be provided.
However, because nozzles in a number equivalent to the number of scan lines are used, in order to record an image with, for example, a dot density of 300 dpi on a 18-inch wide recording sheet, then 5,400 main scan lines are needed. Accordingly, 5,400 nozzles are required even in a monochromatic recording device, and 21,600 nozzles are required in a multicolor recording device that prints in a four colors of ink.
It is possible to realize this type of plural nozzle arrangement for producing an on-demand type ink jet recording device having a high nozzle density. However, a break down in only one of the multiplicity of nozzles causes a fatal problem for the head because a corresponding scan line will be unrecordable so that information that should be recorded will be lost.
Such a nozzle break down can be caused by a variety of reasons, such as an inability to eject ink droplets due to a clogged nozzle orifice or an air bubble in the nozzle, or a bend in the ink ejection direction associated with a half-clogged nozzle orifice or a non-uniform leak of ink to the area around the nozzle orifice. Because it is extremely difficult to regularly prevent these types of break-downs in the plural nozzles during operations, it has been difficult to insure reliability of recording.
Also, there is a problem relating to insuring quality of recorded images. That is, it is difficult to produce a plurality of nozzles with the same dimensions. The ink ejection characteristics of the nozzles can vary because of poor uniformity in production and other reasons.
For example, when ink droplets ejected from adjacent nozzles have a significant lack uniformity in shape, size, and the like, recording distortions, such as line distortions and density distortions, are generated. It is possible in serial type recording heads to make the poor uniformity of ink droplet size less striking by changing the scan region of the recording head. However, the line type recording head that is used fixed in place cannot be used if the recording head has nozzles with poor uniformity because the adjacent nozzles are fixed in place. On the other hand, production yield is extremely poor when producing recording heads with nozzles uniform to a level sufficient to not be problematic. Also, even if the nozzle characteristics are uniform at first, the ejection characteristics of adjacent nozzles can vary for some reasons during operations. This is a problem related to insuring recording quality.
U.S. Pat. No. 5,975,683, which corresponds to Japanese Patent Application Publication No. HEI-8-332724, discloses a line scan type ink jet recording device that manipulates ink droplets using an electric field. This device uses an electric field to deflect ejected ink droplets in the left or right directions to increase the number of dots in the horizontal direction within a single pixel, and to form higher-resolution images. This device will be described in detail with reference to the attached drawings.
A print head 18 shown in FIG. 1 uses an actuator 11 to eject ink droplets 10 from an opening 13 toward a print surface 15. At this time, the positive ions in the ink react to a high negative voltage (−1,000V) of an electrode 14, which is provided behind the print surface 15, and gather in ink surfaces 12. When the ink droplets 10 separate from the ink surfaces 12, the ink droplets 10 are charged to a positive charge. A pair of direction control electrodes 16, 17 are provided on either side of each opening 13. With this configuration, by developing a voltage of −100V at the direction control electrode 16 and a voltage of +100V at the direction control electrode 17, the ink 10 ejected from the openings 13 can be deflected in accordance with well-known laws of static electricity, so the ink 10 flies in directions indicated by arrows in the drawing. Also, by developing a voltage of +100V at the direction control electrode 16 and a voltage of −100V at the direction control electrode 17, then the ink 10 can be deflected to the opposite direction. By developing an electrical bias of 0V at both of the direction control electrodes 16, 17, then the ink droplets 10 fly without being deflected leftward or rightward. By controlling the direction control electrodes 16, 17 in this manner, as shown in FIG. 2, three dots including a right-side dot, a central dot, and a left-side dot can be formed within a single pixel so that an image with high resolution in the horizontal direction can be formed.
However, a deflection electric field control method that controls an electric field between the direction control electrodes 16, 17 and the print surface 15 in this way cannot control deflection of each ink droplet independently. This is because if any ink droplets which has been previously ejected and deflected exist within a presently generated deflection field, the presently generated deflection filed operates on such previously ejected and deflected ink droplets also. For this reason, the device has poor independent deflection operation, which is inconvenient for high-speed recording and for recording efficiency.
This type of recording device does not differ from the above-described device with regards to generating unrecordable scan lines and losing information that should be recorded when even a single nozzle breaks down.